The present invention relates to a method for preparing polyether glycols. In particular, it relates to the alcoholysis of polytetrametylenene ether acetate(PTMEA) in the presence of a mixed metal oxide as a catalyst.
Polyether glycols, such as polytetramethylene ether glycols (PTMEG), are used as starting materials for spandex fibers, thermoplastic urethane (TPU) and copolyester ether (COPE). As TPU prepared by using polyether glycols as raw materials have superior elasticity, water resistance, abrasion resistance and blood and physiology compatability, they have become a very important raw material for special purpose use TPU.
The conventional manufacturing process for polyether glycols involves polymerizing cyclic ether, such as tetrahydrofuran, by a ring-opening process in the presence of a strong liquid or solid acid as a catalyst, followed by hydrolysis or alcoholysis to form hydroxy group end-capped polyether glycols. The above manufacturing process has been disclosed in U.S. Pat. Nos. 2,691,038 and 4,163,115. In addition, U.S. Pat. No. 5,344,964, discloses a method for preparing ester end-capped polyalkylene ether, in which tetrahydrofuran and acid anhydride are catalyzed by a solid acid catalyst to form polytetramethylene ether acetate (PTMEA). The resulting PTMEA is then subjected to alcoholysis to form PTMEG.
U.S. Pat. No. 4,153,786 discloses a method for preparing ester end-capped copolyether glycols. The method includes copolymerizing tetrahydrofuran and alkylene oxide or cyclic acetal in the presence of a polymeric catalyst containing .alpha.-fluoro sulfonic acid groups and an acetic anhydride.
Conventional methods for preparing polyether glycols or copolyether glycols from polyether acetates use alkali catalysts. For example, in U.S. Pat. No. 4,230,892, polyether acetates are subjects to alcoholysis in a slurry reactor in the presence of oxides or hydroxides of calcium, strontium, and barium as catalysts. However, as the solid catalysts are weak mechanically, and thus break down into powder after the reaction, it is rather difficult to recover said catalysts by filtering. U.S. Pat. No. 4,584,414 discloses a method for preparing polyether glycols in which hydroxides or alkoxides of alkali metals are used as catalysts. However, as these kinds of catalyst, when used, are dissolved in alcohols prior to the alcoholysis, it is difficult to separate the used catalysts from the final product.